Liquid crystal display devices have been used for clocks, calculators, household electric appliances, measuring instruments, panels for automobiles, word processors, electronic organizers, printers, computers, televisions, etc. Typical examples of a liquid crystal display mode include a TN (twisted nematic) mode, an STN (super twisted nematic) mode, a DS (dynamic scattering) mode, a GH (guest-host) mode, an IPS (in-plane switching) mode, an OCB (optically compensated birefringence) mode, an ECB (electrically controlled birefringence) mode, a VA (vertical alignment) mode, a CSH (color super-homeotropic) mode, and FLC (ferroelectric liquid crystal). Examples of a driving method include static driving, multiplex driving, passive matrix driving, and active matrix (AM) driving performed using TFTs (thin film transistors), TFDs (thin film diodes), and the like.
In an IPS mode, an ECB mode, a VA mode, a CSH mode, or the like among these display modes, a liquid crystal composition having negative Δ∈ is used. In particular, a VA mode by AM driving is used for display devices required to have high-speed response and a wide viewing angle, such as televisions.
A liquid crystal composition containing the following liquid crystal compounds (A) and (B) having a 2,3-difluorophenylene skeleton (refer to PTL 1) has been disclosed as a liquid crystal composition having negative Δ∈.

This liquid crystal composition contains liquid crystal compounds (C) and (D) as liquid crystal compounds whose Δ∈ is substantially zero. However, a sufficiently low viscosity has not been achieved in liquid crystal compositions required to have high-speed response for liquid crystal televisions or the like.

A liquid crystal composition containing a liquid crystal compound (E) has been disclosed. There have been proposed a liquid crystal composition containing the liquid crystal compound (E) together with the liquid crystal compound (D) to achieve a low refractive index anisotropy Δn (refer to PTL 2) and a liquid crystal composition to which a liquid crystal compound (F) is added to improve the response speed (refer to PTL 3).

A liquid crystal composition containing a liquid crystal compound (G) and the liquid crystal compound (F) has also been disclosed (refer to PTL 4). However, a higher response speed has been required.

A liquid crystal composition containing the liquid crystal compound (A), the liquid crystal compound (G), and a liquid crystal compound whose Δ∈ is substantially zero and which is represented by formula (I) in a combined manner has been disclosed (refer to PTL 5). In the production process of liquid crystal display devices, however, an extremely low pressure is required when a liquid crystal composition is injected into a liquid crystal cell. Therefore, a compound having low vapor pressure is volatilized and thus it is believed that the content of such a compound cannot be increased. Consequently, in the liquid crystal composition, the content of the liquid crystal compound represented by the formula (I) is limited, and thus the liquid crystal composition exhibits high Δn, but unfavorably has a considerably high viscosity.

Furthermore, a liquid crystal composition containing a compound having a terphenyl structure subjected to substitution with fluorine has also been disclosed in PTL 6 and PTL 7.
It has been disclosed in PTL 8 that the response speed of a homeotropic liquid crystal cell is improved by using a liquid crystal material having a large index represented by (formula 1), but the improvement is not sufficient.[Math. 1]FoM=K33·Δn2/γ1  (Formula 1)                K33: elastic constant        Δn: refractive index anisotropy        γ1: rotational viscosity        
In liquid crystal compositions required to have high-speed response for liquid crystal televisions or the like, the following has been required: the refractive index anisotropy (Δn) and the nematic phase-isotropic liquid phase transition temperature (Tni) are not decreased, the viscosity (η) is sufficiently decreased, the rotational viscosity (γ1) is sufficiently decreased, and the elastic constant (K33) is increased.